The invention relates to a radiation-polymerizable mixture which contains as the essential constituents:
(a) a polymeric binder, PA1 (b) an acrylic or alkacrylic acid derivative polymerizable by free radicals and having a boiling point above 100.degree. C. under normal pressure and PA1 (c) a compound or a combination of compounds, which is capable of initiating the polymerization of the compound (b) under the action of actinic radiation. PA1 (a) a polymeric binder, PA1 (b) an acrylic or alkacrylic acid derivative polymerizable by free radicals and having a boiling point above about 100.degree. C. under normal (atmospheric) pressure, and PA1 (c) a compound or a combination of compounds, which is capable of initiating the polymerization of the compound (b) under the action of actinic radiation. PA1 Z is 0 or NH, PA1 R.sup.1 is H or alkyl, PA1 R.sup.2 is alkyl, alkenyl, cycloalkyl, aryl, aralkyl or SO.sub.2 R.sup.3, PA1 R.sup.3 is alkyl, alkenyl, cycloalkyl, aryl, aralkyl or aryloxy, PA1 k is a number from 3 to 20, PA1 l is a number from 0 to 20, PA1 m is a number from 2 to 20, PA1 n is a number from 1 to 20 and PA1 p is a number from 2 to 10. PA1 (a) a polymeric binder, PA1 (b) acrylic or alkacrylic acid derivative polymerizable by free radicals and having a boiling point above 100.degree. C. under normal pressure, and PA1 (c) a compound or a combination of compounds, which is capable of initiating the polymerization of the compound (b) under the action of actinic radiation, and, if appropriate, a cover sheet, which can be peeled off, on the free side of the photoresist layer and which adheres less strongly to the layer than the temporary support. PA1 Q is --CO--C.sub.p H.sub.2 p--Z-- or --C.sub.k H.sub.2k O--, PA1 Z is O or NH, PA1 R.sup.1 is H or alkyl, PA1 R.sup.2 is alkyl, alkenyl, cycloalkyl, aryl, aralkyl or SO.sub.2 R.sup.3, PA1 R.sup.3 is alkyl, alkenyl, cycloalkyl, aryl, aralkyl or aryloxy, PA1 k is a number from 3 to 20, PA1 l is a number from 0 to 20, PA1 m is a number from 2 to 20, PA1 n is a number from 1 to 20 and PA1 p is a number from 2 to 10. PA1 (a) a polymeric binder, PA1 (c) a compound or a combination of compounds, which is capable of initiating the polymerization of the compound (b) under the action of actinic radiation. PA1 Q is --CO--C.sub.p H.sub.2p --Z-- or --C.sub.k H.sub.2k O--, PA1 Z is O or NH, PA1 R.sup.1 is H or alkyl, PA1 R.sup.2 is alkyl, alkenyl, cycloalkyl, aryl, aralkyl or SO.sub.2 R.sup.3, PA1 R.sup.3 is alkyl, alkenyl, cycloalkyl, aryl, aralkyl or aryloxy, PA1 k is a number from 3 to 20, PA1 l is a number from 0 to 20, PA1 m is a number from 2 to 20, PA1 n is a number from 1 to 20 and PA1 p is a number from 2 to 10. PA1 (A) an unsaturated carboxylic acid, PA1 (B) an alkyl methacrylate with at least 4 carbon atoms in the alkyl group, and PA1 (C) an additional monomer which is capable of copolymerization with monomers (A) and (B) and which has a corresponding homopolymer characterized by a glass transition temperature of at least 80.degree. C., preferable at least 100.degree. C.
The mixture is suitable in particular for the preparation of photoresists, especially those which can be prepared and processed by the dry resist process.
Mixtures of the above-mentioned type are known. In U.S. Pats. No. 3,887,450 and No. 3,953,309, photopolymerizable mixtures for use in the dry resist process are described, which can be developed with aqueous-alkaline solutions and, as the polymerizable compounds, preferably contain exclusively those having two or more polymerizable ethylenically unsaturated groups.
Similar mixtures are known from European Patent Application No. 128,014, which additionally contain a mono-unsaturated polymerizable compound, especially an aryloxypolyalkoxyalkyl (meth)acrylate. This addition is intended to improve the flexibility, tackiness and developability of the layers; stripping of the exposed layer areas is thus also facilitated.
German Offenlegungsschrift No. 3,441,787 has disclosed mixtures of the same type and applicability, which contain mono-unsaturated or polyunsaturated monomers, of which at least one contains an aromatic OH, SH or sulfonamide group. These mixtures are distinguished in particular by ready strippability after exposure.
In dry photoresist layers, it is generally customary to use monomers which contain urethane groups. Mixtures of this type are described, for example, in U.S. Pats. No. 3,850,770, No. 4,019,972, No. 4,088,498, No. 4,250,248 and No. 4,387,139. In all these cases, the mixtures contain polyunsaturated compounds, in most cases di-unsaturated compounds.
U.S. Pat. No. 3,783,151 has disclosed similar mixtures based on polyunsaturated polymerizable compounds which contain urethane groups and which are used for the preparation of radiation-curable surface coatings and printing inks. The urethane groups can be introduced by reaction with monovalent or polyvalent isocyanates. If monovalent isocyanates are employed, they are always reacted with polyunsaturated monomers, for example with pentaerythritol triacrylate.
The dry photoresist materials described above and containing monofunctional unsaturated compounds admittedly have improved flexibility and strippability in the exposed state. However, they have other disadvantages which restrict their usefulness in practice. Thus some of the monomers tend to crystallize, and in other cases the exposed layers are unduly brittle or have inadequate adhesion to copper in the unexposed state.